CISCO CISCO HuaWei CISCO Multilevel TRILL allows the interconnection of multiple TRILL networks to form a larger TRILL network without proportionally increasing the size of the IS-IS LSP DB. In this document, an approach based on default route concept is presented. Also, presented in the document is a novel method of constructing multi- destination trees using partial nickname space. Methods presented in this document are compatible with the RFC6325 specified data plane operations.